Decolorizing film



Patented Jan. 14, 1930 UNITED (STATES PATEN QFFHQE EDMUND IB. MIDDLETON, 0F PARIJN, NEW JERSEY, ASSIGNOR TO E. I. DU PON'I DE NEMOURS 8c COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELA- WARE DECOLORIZING FILM No Drawing.

This invention relates to a process of removing dye from tinted cellulosic materials and comprises treating the material first with a bleaching agent and then with a dye solvent which preferably contains a decolorizing substance. F

In the utilization or reclamation of scrap or waste pieces of cellulosic materials such as tinted celluloid or colored photographic film base, etc., the presence of the tint or dye is generally objectionable and the partial or total removal of the color is often advisable before the materials are to be utilized.

It is the object of this invention to provide a process for removing the dye from cellulosic materials in an efiicient and economical manner without materially affecting the cellulosic base materials. Other objects and advantages will appear from the description.

The decolorization of the cellulosic material according to the present invention is carried out in several steps. In general, the dye is removed from the tinted cellulosic substance by first treating the substance with a bleaching or an oxidizing agent which destroys all or most of the dye. The bleached .material is then treated with a liquid which is a solvent for, the bleached dye but is not a solvent for the" cellulosic material. This liquid preferably contains suspended in. it a suitable decolorizing material such as bone char or activated charcoal. In this Way any of the dye remaining after the bleaching treatment is removed and the liquid solvent is decolorized at practically the same time.

This invention will be described more specifically in connection with the decoloriza tion of photographic film base, to which it is particularly adapted, but is not limited to this application of the process. The tinted cellulosic photographic film base is usually dyed upon the under surface and generally is'surfaced with gelatine. An illustration of the procedure for decolorizing the film is as follows:

The film is generally subjected to a washing treatment whereby most of the gelatine surfacing material is dissolved off by means of water or other washingliquid. After this Application filed'December 31, 1925. Serial No. 78,701.

treatment, the washed film base is subjected to a bleaching operation.

As a suitable bleaching or oxidizing agent, a water solution of a hypochlorite is made up containing about one-tenth of one per cent of available chlorine which may be liberated by the addition bf a suitable acid. The washed film is immersed in a bleaching bath of this solution until it is practically colorless or has been bleached to the desired extent. The bleaching solution may be acidified with any suitable acid immediately before or immediately after the immersion of the colored film. Or, if desired, the film may be allowed to soak in the hypochlorite solution before it is acidified. The bleaching treatment destroys most of the dye and in addition removes any gelatine remaining on the film base as a substratum or from incomplete washing.

After the film is bleached, it is removed from the bleaching solution and is immersed in ethyl alcohol containing decolorizing carbon such as bone char or activated charcoal. The bleached film base is soaked in the alcohol containing the suspended carbon until it is free of all color. Thirty minutes soaking is usually sufficient to remove all traces of dye. The film base is removed from the alcohol, allowed to drain, and is washed with water. Theadhering carbon is easily washed away, whereas with the unbleached film, some of the carbon would adhere firmly because of the gelatine present on the film. Fresh decolorizing carbon is added from time to time to take the place of exhausted carbon. The exhausted carbon can be reactivated in any of the well known ways. Instead of ethyl alcohol, any other liquid may be used which is a solvent for the dye but Which does not dissolve'the film.

Instead of using a hypochlorite bleaching bath the dyed materials may be subjected to the action of moist gaseous chlorine from any suitable source. Other bleaching or oxidizing agents such as hydrogen peroxide may be used with good results.

The process of decolorization described generally takes place with suflicient rapidity at ordinary room temperatures to dispense bleaching of film or tinted cellulosic material,

serves a double function. The solvent not only extracts the remaining dye from the material, but it also dissolves many objectionable colorless compounds, probably chlorinated compounds resulting from the reaction of chlorine with dyes, softeners and residual solvents. Many of these substances, if present, make the materials unsuitable forreclamation purposes: Ordinarily their removal would necessitate one or more separate steps or treatments, but according to the present invention these objectionable compounds are removed in the solvent treatment. I claim:

1. The process of decolorizing dyed cellulosic films which comprises treating the films with a bleaching agent to bleach the dye and soaking the bleached product in a liquid which is a solvent for the bleached dye but is not a solvent for the cellulosic material.

'2. The process of decolorizing dyed cel- 7. The process of removing dye from photographic film base which comprises bleaching the dye with chlorine and treating the bleached film with a bleached dye solvent which is a non-solvent for the film.

In testimony whereof I affix my signature.

EDMUND B. MIDDLETON.

lulosic films which comprises treating the I films with a bleaching agent to bleach the dye and soaking the bleached product in a liquid which is a solvent for the bleached dye but is not a solvent for the cellulosic material, the liquid having a decolorizing material suspended therein.

3. The process of decolorizing dyed cellulosic films which comprises treating the films with a bleaching agent to bleach the dye and soaking the bleached product in a liquid which is solvent for the bleached dye but is not a solvent for the cellulosic material, the liquid having decolorizing carbon suspended therein.

4. The process of decolorizing dyed cellulosic films which comprises bleaching the dye with chlorine and soaking the bleached product in a liquid which is a solvent for the bleached dye but is not a solvent for the cellulosic material.

5. The process of decolorizing dyed cellulosic films which comprises bleaching the dye with chlorine and soaking the bleached product in a liquid which is a solvent for the bleached dye but is not a solvent for the cellulosic material, the liquid having a decoloriz ing material suspended therein.

6. The process of removing dye from photographic film base which comprises bleaching the dye and treating the bleached film with a bleached dye solvent which is a non-solvent for the film. 

